Researchers assess radiation exposure in obese patients

A group of US researchers has quantified the amount of radiation obese patients receive when undergoing routine medical scans.

Results published today, 6 April, by IOP Publishing in the journal Physics in Medicine & Biology, have shown that, when undergoing a CT scan, a forced change of operation parameters for obese patients results in an increase of up to 62 per cent in organ radiation exposure compared to lower weight patients.

The researchers, from Rensselaer Polytechnic Institute, hope this new study will help optimise CT scanning procedures to produce safe but effective medical images.

Lead author of the study, Dr Aiping Ding, said: “When a morbidly obese patient undergoes a CT scan, something known as the tube potential needs to be increased to make sure there are enough x-ray photons passing through the body to form a good image. So far, such optimization has been done by trial and error without the use of patient-specific quantitative analysis.”

When the researchers simulate the increase, the calculated doses of radiation reaching an obese patient’s organs increase by 62 per cent in males and 59 per cent in females.

Their initial results confirmed why the tube potential is often increased: a scan of the chest, abdomen and pelvic area of obese patients, without adjusting the tube potential, showed that organs deep within the abdomen received 59 per cent less radiation compared to normal weight patients, due to the excess fat tissues.

Such a reduced dose could negatively affect the image quality unless the tube potential and tube current are adjusted accordingly.

Results were obtained by creating 10 (5 male, 5 female) computerised phantoms with a body mass index (BMI) ranging from 23.5 kg/m2 (normal weight) to 46.4 kg/m2 (morbidly obese) ¾ such a detailed model of obese patients has not been used before.

Phantoms are specifically designed physical or simulated objects that can be experimented with in the field of medical imaging for evaluating, analysing and tuning the performance of various devices. This study used computer-simulated deformable phantoms which were put through a CT scanning computer model to calculate the dose of radiation exposed to each one.

The phantoms were unique in that they not only accounted for a large number of organs, but also modelled two types of fat: the subcutaneous adipose tissue (SAT) under the skin and the visceral adipose tissue (VAT) that lies deeper in the body and sits around the organs. This gave the researchers a much clearer idea about the amounts of radiation reaching different organs.

The prevalence of overweight and obese individuals has increased markedly over the past 20 years; a recent survey suggests that nearly 60 per-cent of the adult American population can be diagnosed as being clinically overweight or obese.

Given this alarming trend and the health risks associated with obesity, it is no surprise that an increasing number of overweight or obese individuals are entering radiology clinics.

“We hope that this very timely set of data will be integrated with previous work for normal size adult and child patients to form a comprehensive database to support a software package called VirtualDose that will enter clinical testing this summer.

“Such a tool could be used to analyze radiation exposure trends in a clinic and to study how to optimize the image quality for a large population of patients,” said Professor X George Xu, the senior corresponding author of the study.

The study, undertaken by researchers at Rensselaer Polytechnic Institute – the oldest technological university in English speaking countries – is funded by a grant from the National Institute of Health.